Researchers from Imperial College London and the University of Glasgow - both in the United Kingdom - reveal how participants who consumed milkshakes containing a supplement called inulin-propionate ester were less likely to crave foods high in calories.

The supplement works by increasing production of the compound propionate in the gut, which previous studies have shown is released naturally when the fibre inulin - found in fruits and vegetables such as artichokes,bananas, and asparagus - is digested.

Inulin is known to reduce appetite by slowing digestion and increasing fullness, and it is already available as a dietary supplement. Previous studies have shown that propionate also reduces appetite, though exactly how has been unclear.

For this latest study, senior author Prof. Gary Frost, of the Department of Medicine at Imperial, and colleagues set out to determine exactly how propionate reduces appetite, and whether inulin-propionate ester - a combination of inulin and propionate - might be more effective than inulin alone for scaling down food intake.

Inulin-propionate ester reduces brain activity linked to food reward

The team enrolled 20 healthy-weight men to the study. Some of the men consumed a milkshake containing inulin-propionate ester, while others drank a milkshake containing inulin alone.

After drinking the milkshakes, the men were asked to view pictures of low-calorie foods (such as salad and fish) or high-calorie foods (such as cake and pizza). As they did so, their brain activity was monitored using functional magnetic resonance imaging (fMRI).

Compared with the men who drank the inulin-only milkshakes, those who consumed the milkshakes containing inulin-propionate ester had reduced activity in reward centers of the brain called the caudate and the nucleus accumbens, but only when they viewed images of high-calorie foods.

The caudate and the nucleus accumbens are areas of the brain that have been associated with food motivation and cravings.

Additionally, the researchers found that men who consumed the milkshakes containing inulin-propionate ester rated the high-calorie foods as less appealing than those who consumed the inulin-only milkshakes.

Next, the researchers gave the men a bowl of pasta with tomato sauce and told them to consume as much as they wished.

They found the men who consumed the milkshakes containing inulin-propionate ester ate around 10 percent less pasta than those who consumed the inulin-only milkshakes.

Study 'fills in a missing piece of the jigsaw'

The authors say these findings build on previous research, in which they found that people who consumed a daily inulin-propionate ester supplement gained less weight over a 6-month period than those who consumed inulin alone.

Now, the researchers have uncovered an explanation for that finding. "This study is filling in a missing bit of the jigsaw - and shows that this supplement can decrease activity in brain areas associated with food reward at the same time as reducing the amount of food they eat," says Prof. Frost.

What is more, the team says the finding could explain why some people are more susceptible to weight gain than others - they might have lower propionate production.

"This study illustrates very nicely that signals produced by the gut microbiota are important for appetite regulation and food choice. This study also sheds new light on how diet, the gut microbiome and health are inextricably linked adding to our understanding of how feeding our gut microbes with dietary fiber is important for healthy living." - Study co-author Dr. Douglas Morrison, University of Glasgow

Based on their findings, the researchers believe adding inulin-propionate ester to foods could reduce people's urge to consume foods high in calories, which could prove an effective way to combat the current obesity epidemic.